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Air quality requirements - How do HEPA Filters keep air clean?

In a medical environment, effective disinfection and sterility are critical to maintaining patient health, while reducing the chance of harming patients with compromised or weak immune systems.

It’s exceptionally important that the air found inside hospitals and healthcare facilities is kept clean and free of contaminants. This is because air containing particulates can cause or aggravate respiratory conditions.

In addition, infectious diseases, bacteria, germs and viruses can all be transferred by indoor air - to patients with already damaged immune systems.

HEPA Filters South Africa - Types of Air Filters

HEPA Filters - Air Quality Regulatory Requirements

Furthermore, HEPA filters are also used to achieve and maintain air quality regulatory requirements in cleanrooms and pharmaceutical manufacturing facilities. Regulatory standards such as the ISO 14644-3 has clearly defined grades.

HEPA filters are classified as H12, H13 or H14. This classification refers to the efficiency of the filter media with reference to the Most Penetrating Particle Size. “MPPS” which are particles of 0,3µm in size. An H14 HEPA filter will trap 99,999% of all 0,3µm particles.

HEPA filtration is therefore a powerful defence mechanism against particulates and biological contaminants, but how exactly does this type of air filtration work?

High-Efficiency Particulate Air (HEPA)

HEPA filters are composed of a mat of randomly arranged fibres. These fibres are commonly made up of fiberglass with diameters between 0.5 and 2.0 micrometres, with air spaces between HEPA filter fibres typically much greater than 0.3 μm.

HEPA filtration operates mechanically unlike ionic and ozone filtration which utilise negative ions and ozone gases. Therefore the possibility of potential pulmonary side-effects such as asthma and allergies is much lower with HEPA air purifiers.

A common assumption is that HEPA filters act like sieves, however, these filters are designed to target much smaller pollutants and particles, trapping them through a combination of the following three mechanisms:


Occurs when particles following an air stream’s line of flow come within one radius of a fibre and become stuck to it.


Occurs when larger particles cannot avoid fibres while following the curving contours of the air stream. They are then forced to directly embed themselves in a fibre. Occurrence increases with diminishing fibre separation and higher air flow velocity.


Occurs as a result of a collision with gas molecules by the smallest particles, particularly those below 0.1 µm in diameter. These particles are then obstructed and delayed through the filter. This effect is similar to Brownian motion and increases the probability that a particle will be stopped by either the interception or impaction mechanism. This mechanism becomes dominant at lower air flow velocities.

Interception and Impaction predominate above 0.4 μm, while Diffusion predominates below the 0.1 μm diameter particle size.

Vivid Air – HEPA Filters and Air Filtration South Africa

In hospitals and healthcare centres, HEPA filters must be checked and changed frequently to avoid contaminants building up.

It’s vital that your HEPA filtration system be designed, installed and maintained by qualified professionals.

Vivid Air are stockists of several types of HEPA filters for various applications and have years of experience with installation and management.

Contact us, for more information about HEPA filters and air filtration system requirements.

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